Did Dark Matter Cause Many of Earth's Mass Extinctions?

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The Milky Way's galactic plane
The thin disc of the Milky Way's galactic plane is believed to contain high levels of dark matter.

Hewholooks [CC by 3.0] / Wikimedia

Most of us are familiar with the story of what likely killed the dinosaurs: An asteroid or comet impacted the Earth 66 million years ago, causing what is called the Cretaceous–Paleogene extinction event. But a new study by Michael Rampino of New York University suggests that this story might be incomplete.

Rampino has proposed that dark matter — a hypothetical, invisible kind of matter that is theorized to make up most of the matter in the universe — may have been what really caused the dinosaurs to die, reports NYU News. In fact, he suggests that dark matter may be to blame for many of Earth's mass extinctions — and it could one day threaten us too.

The theory rests on the idea that dark matter is more concentrated along our galaxy's galactic plane, the relatively thin disc where most of the Milky Way's matter resides. Not only does our solar system rotate around this disc (it takes roughly 250 million years for us to make it all the way around), but it also bobs up and down, kind of like a buoy. This bobbing causes us to pass directly through the galactic plane about every 30 million years.

Interestingly, fossil records show us that extinction events also tend to happen in 26-30 million year cycles. So, Rampino wondered: Might dark matter be the culprit? He has proposed two ways that dark matter may be indirectly causing these extinction events. First, as our solar system passes through the galactic disc, the dark matter concentrated there might disturb the pathways of comets, possibly increasing the odds that they eventually collide with Earth. This might even have been what triggered the impact that caused the extinction of the dinosaurs.

A second possibility is that as Earth passes through the galactic plane, dark matter gets caught in the planet's gravity, eventually accumulating in the core. As the dark matter particles meet, they annihilate each other, producing heat. This, in turn, might trigger events such as volcanic eruptions, mountain building, magnetic field reversals, and changes in sea level — which, incidentally, also show peaks roughly every 30 million years.

“We are fortunate enough to live on a planet that is ideal for the development of complex life,” said Rampino. “But the history of the Earth is punctuated by large scale extinction events, some of which we struggle to explain. It may be that dark matter – the nature of which is still unclear but which makes up around a quarter of the universe – holds the answer. As well as being important on the largest scales, dark matter may have a direct influence on life on Earth.”

At the very least, Rampino's research puts the timescale of Earth and its movements through the heavens in a new perspective. In the future, it may be useful for theorists to take a step back and consider the astrophysical events that impact our solar system when seeking to explain geological or biological events here on Earth.

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